1. Field of the Invention
The present invention relates to a binocular, and more particularly, to a binocular of horizontally moved type.
2. Description of the Prior Art
Typically, the eyepieces and the objective lenses of a binocular provided at the front and rear ends of the left and right lens barrels are exposed to the outside. For this reason, if the binocular is left uncovered when not used, dirt such as dust and oil is apt to adhere to the lens surfaces, and the lenses may be scratched when the dirt is wiped off. To solve such a problem, typically, four lens caps (a pair for each of the front and rear ends) for covering the lens surfaces are prepared for a binocular in correspondence with the eyepieces and the objective lenses. When the binocular is not used, these caps are attached at the front and rear ends of the lens barrels to protect the eyepieces and the objective lenses.
However, as many as four lens caps are necessary for one binocular as described above and the lens caps which are maintained attached only by a pressure contact with the peripheries of the lens barrels when they are attached to the lens barrels are readily disconnected only by slight vibration or external force. For this reason, even if not all of them are lost, some of them may be lost without being noticed.
In addition to the problem that the lens caps are readily lost, these lens caps are inconvenient such that the pupil distance cannot be adjusted unless the caps are detached every time the binocular is used and that it is necessary to keep the detached caps in some way.
A typical conventional binocular is such that one lens barrel is attached to a central shaft provided to protrude from a side of the other lens barrel to be rotatable within a predetermined angle range, that a focusing operation member is provided coaxially with the central shaft to be rotatable by a predetermined number of rotations, that the pupil distance is adjusted by folding the lens barrels in two at the central shaft, and that focusing is performed by rotating the focusing operation member with the lens barrels being held by the hands.
In the case of a conventional binocular of such a folded type, since it basically takes a symmetrical form, the distances between the focusing operation member arranged in the center and the left and right lens barrels are the same, so that focusing, which is performed by rotating the focusing operation member after the pupil distance is adjusted, can be performed without hindrance with any of the right and left hands. Thus, there is no difference in operability according to whether the user is right-handed or left-handed.
However, in the binocular of folded type, it is necessary to satisfy the following two contradicting conditions: that the left and right lens barrels are not shifted from the adjusted positions after the pupil distance has been adjusted; and that the operation to fold the left and right lens barrels is smoothly performed. For this reason, the adjustment of a force to fasten one lens barrel to the central shaft is difficult and it is structurally difficult to provide an automatic focusing function.
As prior arts to solve this problem, for example Japanese Published Utility Model Application No. S57-34486 and Japanese Laid-open Patent Application No. S55-161205 disclose so-called binoculars of horizontally moved type where, to adjust the pupil distance, a focusing operation member is arranged in one lens barrel and the other lens barrel is linearly movable perpendicularly to the optical axis toward the one lens barrel.
The horizontally moved type binocular is advantageous over the folded type in that no screws are necessary for connecting the left and right lens barrels requiring fastening and adjustment and that the automatic focusing function can be provided. However, since one of the lens barrels is slid to adjust the pupil distance, according to the position to which the focusing operation member is attached, generally, it is inconvenient for a left-handed person to use the binocular.
Specifically, in Japanese Laid-open Patent Application No. S55-161205, a rotary knob serving as the focusing operation member is provided to protrude only from one surface and to lean toward one of the lens barrels. Japanese Published Utility Model Application No. S57-34486 does not specifically show any focusing operation member.
Referring to FIG. 1, there is schematically shown an example of a binocular where the focusing operation member is provided at the same position as that of Japanese Laid-open Patent Application No. S55-161205. As is apparent from this figure, in an arrangement where a focusing operation member 11 is arranged to protrude only from the center of the upper surface in a housed condition where the distance between the left and right lens barrels 1 and 2 is minimum, when a left-handed person uses the binocular under a condition where the pupil distance has been adjusted by sliding the left lens barrel 2 which is movable, the vicinity of the portion between the bases of the thumb and the forefinger interferes with the left lens barrel 2 when the fingers are reached to the focusing operation member 11 to perform focusing. This is very uncomfortable.
In an arrangement where the focusing operation member 11 is thus arranged only on one surface, since the upside and the downside of the binocular is fixed, when the binocular is operated with the right hand, the operation member 1 is located close to the bases of the fingers. However, when the binocular is operated with the left hand, not only the focusing operation member is farther from the fingers but a distance A to the focusing operation member 11 varies according to the pupil distance. Thus, the operability differs according to whether the user is right-handed or left-handed In particular, the operability may greatly be inferior for left-handed persons.
All this adds up to the following: In a conventional binocular asymmetric in the left and right direction, for example in a binocular where the focusing operation member is provided on the left or right side, the operability remarkably differs according to whether the user is right-handed or left-handed. Such an inconvenience is a great problem under the present circumstances where the size of the binocular is increasingly reduced so that the user can hold it only with one hand.
As a solution to the problem of the difference in operability according to whether the user is right-handed or left-handed, it is considered to prepare two kinds of binoculars: one is for right-handed persons and the other, for left-handed persons. However, not only this increases the manufacture cost but when one kind of the binocular is used by a plurality of persons, the above-described problem will result. Thus, this cannot be a radical solution to the problem.
Typically, in a binocular, the dioptric power is adjusted to meet the user's eyesight by moving a part of the optical systems, e.g. eyepieces and objective lenses of the left and right lens barrels. Conventionally, a mechanism for such dioptric power adjustment is provided with a dioptric power adjusting ring interlocked, for example, with the eyepieces of the lens barrels. To adjust the dioptric power, under a condition where the binocular is focused on infinity, the dioptric power adjusting ring is rotated in a plus or a minus direction by a manual operation so that a part of the optical systems is moved along the optical axis together with the movement of the ring.
As another prior art, a binocular provided with an automatic focusing function is known where by driving the optical systems by use of a driving force of a motor, the dioptric power is automatically adjusted only by operating a switch. As a binocular provided with a dioptric power adjusting mechanism of such an automatic controlling method, for example, Japanese Laid-open Patent Application No. H5-11195 discloses a binocular where a means for adjusting the dioptric power is electrically controlled to thereby disable the dioptric power adjustment when the main switch is OFF.
In the former binocular of the manual adjustment type, since the dioptric power adjusting ring is provided at an eyepiece window which is easily reached so that the user can always adjust the dioptric power, when the binocular is not used, the dioptric power may be changed without the user knowing it by unconsciously touching the dioptric power adjusting ring or by another object touching the dioptric power adjusting ring.
The change of dioptric power which can thus occur accidentally is not limited to the binocular provided with the dioptric power adjusting ring. This can occur in a conventional binocular using the manual adjustment method since for reasons of operability, the dioptric power adjustment is arranged to expose outside in such a binocular.
In a binocular like the latter binocular disclosed by Japanese Laid-open Patent Application No. H5-11195 where the dioptric power adjusting mechanism is disabled while the main switch is OFF, the problem that the dioptric power adjusting mechanism is accidentally operated when the binocular is not used is considered to be prevented. In actuality, since an operation member for turning on and off the main switch and a user select switch operation member for the user to arbitrarily change the dioptric adjustment data are provided to be exposed at a portion on the external surface of the binocular where the operation members are easily operated, the operation members are accidentally moved without the user knowing it, which results in the change of dioptric power.
As typical binoculars of pupil distance adjusting type, the following are known: a folded-type binocular where one lens barrel is attached to a central shaft protruding from a side of the other lens barrel to be rotatable within a predetermined angle range and the pupil distance is adjusted by folding the lens barrels in two about the central shaft; and a horizontally-moved type binocular where to adjust the pupil distance, one lens barrel is linearly moved in a horizontal direction perpendicular to the optical axis relative to the other lens barrel. In these typical binoculars, the pupil distance is adjusted by manually moving one lens barrel so that the distance with the other lens barrel increases or decreases.
In the above-mentioned typical binoculars, generally, the pupil distance is reduced to the minimum so that the binocular is compact in the housed condition where the binocular is not used and the pupil distance is adjusted when the binocular is used. In recent years, in many cases, a binocular used for a special purpose such as bird watching as well as a comparatively small size binocular suitable for seeing a play and watching a sport is used exclusively by the owner. In such a case, however, although the binocular is used only by a specific person and the pupil distance is naturally invariable, it is necessary to adjust the pupil distance every time the binocular is taken out of its housing case and used. This is disadvantageous and inconvenient.
As prior arts intended to solve such disadvantage and inconvenience, for example, first, Japanese Laid-open Utility Model Application S48-29838 discloses a pupil distance restricting unit which declines the eyepiece barrels so that a pre-restricted pupil distance is obtained, and secondly, Japanese Laid-open Utility Model Application S50-120450 discloses a pupil distance restricting unit which adjusts the position of declination of a pupil distance restricting ring to decline the lens barrels so that a predetermined pupil distance is obtained.
The pupil distance restricting units of the first and second prior arts are both designed to restrict the distance between the left and right lens barrels within a predetermined distance by stoppers previously set at predetermined positions in adjusting the pupil distance to use the binocular. Therefore, once the positions of the stoppers is set, an optimum pupil distance adjusted condition is always obtained only by increasing the distance between the left and right lens barrels until they are stopped by the stoppers without viewing through the lens barrels.
In the cases of the first and second prior arts, once the pupil distance is set to a predetermined distance, the presence of the stopper saves the trouble of re-adjusting the pupil distance. However, since no driving means is provided for varying the pupil distance from the housed condition to the used condition, it is necessary to perform the operation to increase the distance between the lens barrels until they are stopped by the stoppers while holding the left and right lens barrels by hands. Thus, both hands are occupied with this operation.
To solve such a problem, it is considered to enable an arbitrary and automatic pupil distance adjustment between the housed condition and a position restricted by the stopper through a motor driving as shown in FIG. 2 by using a pupil distance driving mechanism as disclosed by Japanese Laid-open Patent Application No. H5-107441, i.e. by using a mechanism provided with a motor to drive a pupil distance varying mechanism incorporated in the binocular so as to adjust the pupil distance to meet the user's pupil distance and by combining the pupil distance driving mechanism with the pupil restricting unit of the second prior art.
However, in this case, the binocular can merely be designed so that the pupil distance is arbitrarily adjustable between the housed condition where the pupil distance is minimum and the used condition where the pupil distance is set to an optimum distance by operating an operation member provided for pupil distance adjustment, and it is impossible to adjust the pupil distance from the housed condition to a set pupil distance by a momentary operation. For this reason, it is necessary for the user to depress the operation member all the time until the pupil distance is set to the set value.